Alloy



Patented Aug. 31, 1954 ALLOY James M. Lohr, Morristown, N. J., assignorto Driver-Harris Company, Harrison, N. J a corporation of New Jersey NoDrawing. Original a ry 1, 1952. her 19, 1951, Serial No.

1949, Serial No.

2,581,420, dated Janua this application Octo 4 Claims. 1

This invention relates to alloys and more particularly to alloys forelectric resistance units.

In the manufacture of electrical resistance units, an alloy having theproperty of resisting oxidation at high temperature is essential. Thealloys forming the subject matter of this invention are characterized byability to resist oxidation and by a prolonged life, exceeding that ofother known alloys when used under high temperature conditions. Sincethe introduction of nickel-chromium-iron alloys as electric resistanceunits, many developments have occurred that have improved theirresistance to oxidation. In a number of prior patents I have disclosedand claimed various alloying additions of calcium, zirconium andaluminum which greatly improve the life of heating elements. It has alsobeen proposed to add rare earth metals, such as cerium, tonickel-chromium-iron alloys to improve the life of the heating elements.

I have found that when calcium and aluminum as well as rare earth metalsare added to nickelchromium-iron alloys, better results are obtainedthan if the calcium, zirconium, aluminum group or the rare earths areused alone. The present invention is, therefore, directed to theaddition of small quantities of the rare earths with calcium andaluminum to nickel-chromium-iron alloys. I have found that suchcombination of addition elements greatly increases the period of life ofnickel-chromium-iron alloys when employed under conditions where theyare subjected to high temperatures. The alloys forming the subjectmatter of the present invention may also contain small amounts of eithersilicon or manganese or both of these elements. The rare earth metalsmay be added as misch metal" having an approximate composition of 45percent cerium, 30 percent lanthanum, 20 percent ytterbium and didymium.Although it is convenient to add the rare earth metals in the form ofmisch metal," I do not restrict myself to the use of this material asone or more of the rare earth metals may be added singly and its effectis of a similar nature. The additions may be used to advantage with thenickel-chromium-iron alloys of which the best known examples are thealloys of 30 to 70 percent nickel, to 25 percent chromium, balance iron.

This application is a division of my copending application Serial No.117,510, filed September 23, 1949, now Patent No. 2,581,420. The claimsof this application are directed to alloys containing 30 to 50 percentnickel and 10 to 25 percent chromium, and more specifically to alloyscontaining pplication September 23, ,510, now Patent No.

Divided and 2 substantially 35 percent nickel and substantially 20percent chromium.

In the examples hereinafter described, the additions were made to thealloys consisting of substantially 35 percent nickel, 20 percentchromium and balance iron. Rare earth metals, such as misch metal, withcalcium and aluminum may be added to such alloys with or withoutsilicon. The proportions of nickel in such alloys may vary from 30 to 50percent and the chromium from 10 to 25 percent with the balance iron.Employing nickel-chromium-iron alloys of these proportions, I have addedcalcium, aluminum and misch metal in the quantities or amountshereinafter mentioned.

In preparing alloys containing the addition elements above mentioned,the quantities of such addition elements are subtracted from the ironcontent. For example, when additions are made to base alloys containing30 to 50 percent nickel, 10 to 25 percent chromium, the final alloyswill contain 30 to 50 percent nickel, 10 to 25 percent chromium, theaddition elements calcium, aluminum and the rare earth metals in thepercentages hereinafter stated, and the balance iron. While theproportions of calcium, aluminum and rare earth metals may vary withincertain limits, I have found that the best results are obtained whenthese materials are present in the final alloys within the followinglimits:

Percent Calcium .001-20 Aluminum .01-1.0 Rare earth metals Trace-0.50

If the alloys contain manganese, silicon, or carbon, they may be presentwithin the following limits:

Percent Manganese .02-4.0 Silicon .20-3.0 Carbon 0.25 max.

While alloys having the properties desired to a very high degree areobtained within the limits before mentioned, the preferred range ofaddition elements is as follows:

The alloys so prepared have been tested for resistance to oxidation athigh temperature by a modification of the method approved by theAmerican Society for Testing Materials Accelerated Life Test forMetallic Materials, B76-39. In conducting such test, :the silky isproduced in the form or a wire, drawn to a diameter approximately .025"and tested at a temperature of 1950 F., instead of a temperature of 2050R, which is the temperature of the standard ASTM method for testing the60 nickel, 15 chromium alloys, The useful life" in hours for wire ofsubstantially 35 percent nickel, fldparcentnchromium containing calcium,zirconium and aluminum as addition elements, balance iron, is of theorder of 100 hours. The useful life" of the alloys of the presentinvention, according to the above described test, is of the order '0!400 hours. Thus, the useful life is increased around 300 percent overthat of the alloys containing the calcium, zirconium, aluminum groupwhen the rare earth metals are added with calcium and aluminum in theproportions herein-stated.

The alloys are prepared in the usual manner by placing the ingredientsin a bath, heating until the alloying elements become molten and thenpouring. In adding rare earth metals to a molten bath, it is necessaryto add considerably larger quantities than will be found in the castmetal because they vaporize readily and pass out of the bath. In manyinstances, with additions of the rare earth metals only a spectrographictrace of one or more of the rare earth metals is found in the castmaterial. The presence of such traces, however, in combination withcalcium and aluminum, greatly increases the oxidation resistance of thealloys. added in amounts sufficient to leave a residue in the castalloys up to .2 percent but in most instances the use of such amounts isnot necessary.

In the test referred to above the increase or electrical resistance attemperature with time is The rare earth metals maybe 4 plotted and anincrease of 10 percent in resistance is known as the useful life." Thelife of the tiejsted specimen to burn-out is known as total ilclaim:

l. A nickel-chromium-iron alloy consisting substantially of percentnickel, substantially 20 percent chromium, .001 to .20 percent calcium,.01 to 1.0 percent aluminum, a trace to .50 percent of a, rare earthmetal, balance essentially iron.

2. A nickel-chromium-iron alloy consisting substantially of 35 ,percentnickel, substantially 20 percent chromium, .001 to .07 percent calcium,

-01 to .40 percent-aluminum, a trace to .20 percent of a rare'earthmetal, balance essentially iron.

3. A nickelchromium-iron alloy consisting substantially of 35 percentnickel, substantially 20 percent chromium, .00il to .20 percent calcium,.01 to 1.0 percent aluminum, a trace to .50 percent cerium andlanthanum, balance essentially iron.

4. A nickel-chromiumiron alloy consisting substantially of 35 percentnickel, substantially 20 percent chromium, .00 to .07 percent calcium,.01 to .40 percent aluminum, a trace to .20 percent cerium andlanthanum, balance essentially iron.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,941,648 Armstrong Jan. 2, 1934 2,581,420 Lohr Jan. 8, 1952FOREIGN PATENTS Number Country Date 488,926 Great Britain July 12, 1538

1. A NICKEL-CHROMIUM-ION ALLOY CONSISTING SUBSTANTIALLY OF 35 PERCENTNICKEL, SUBSTANTIALLY 20 PERCENT CHROMIUM, .001 TO .20 PERCENT CALCIUM,.01 TO 1.0 PERCENT ALUMINUM, A TRACE TO .50 PERCENT OF A RARE EARTHMETAL, BALANCE ESSENTIALLY IRON.